How many terms of the A.P. 16, 14, 12,.. are needed to give the sum 60? Explain
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Answered by
1
Answer:
We know 16 + 14 + 12 + 10 + 8 = 60
This is the sum of the first five terms of AP 16, 14 ,12....
So the answer is 5 terms.
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Answered by
1
Step-by-step explanation:
A.P. 16, 14, 12,.. are
sum 60
a=16, d=14-16= -2
sn=n/2 (2a+(n-1)d)
60=n/2 (2×16+(n-1)(-2))
120=n (32-2n+2)
120=n (34-2n)
120=n×2 (17-n)
60=n (17-n)
60=17n-n^2
n^2-17n+60=0
n^2-5n-12n+60=0
n (n-5)-12 (n-5)=0
(n-5)(n-12)=0
n=5,12
here the terms either 5 or 12.
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